The mission of NINDS is to reduce the burden of neurological disease - a burden borne by every age group, by every segment of society, by people all over the world." Stroke is the third leading cause of death in the U.S. and the leading cause of long-term disability. Stroke incidence differs between men and women, partly due to the protective effects of estrogen. Currently, there is only one FDA-approved treatment for stroke;Tissue Plasminogen Activator, which can lead to severe brain hemorrhage in up to 7% of treated patients. Recently, differences in cell death pathways between the sexes have been discovered. The goal of this proposal is to characterize these sex differences in order to develop sex-specific therapies to more efficiently treat stroke patients, reducing the public health burden of this disease. Caspase-independent cell death may be a major contributor to cell death in the male brain. However, the mechanism of cell death in the females remains relatively understudied. Recent in-vitro evidence suggests cell death in cultures derived from female neurons occurs predominately via cytochrome c (cyt-c) release from the mitochondria, which dimerizes with Apoptotic Protease Activating Factor-1 (Apaf-1), leading to apoptosome formation, caspase activation and subsequent apoptosis. Treatments that improve stroke outcome in males can paradoxically increase damage in females. In Aim 1 of this proposal we will evaluate the possibility that cell death follows distinct cellular pathways in male and female brain. We will investigate the role of caspase-mediated cell death proteins (XIAP, Apaf-1, Smac/DIABLO, caspases, and cyt-c) in both male and female mice after experimental stroke. Currently, how these caspase-mediated cell death proteins are regulated is unknown. A novel class of molecules, micro-RNAs (miRNAs), post-transcriptionally regulates gene expression. These 22 nucleotide single-stranded RNA molecules bind and inhibit mRNA translation. miRNAs have not been studied in ischemia, but have been implicated in cell growth and apoptosis. Aim 2 hypothesizes that miRNAs may be responsible for the differential regulation of caspase-mediated cell death proteins between the sexes. Dichotomous regulation of apoptotic molecules may play an important role in the sex differences observed in cerebral ischemia. The overall goal of this proposal is to investigate mechanisms underlying sex differences in ischemic cell death.